This invention relates to data processing networks comprising a plurality of data processing stations which can communicate with each other over a common bus.
One such network is described for example in U.S. Pat. No. 4,063,220, in which the common bus is a co-axial cable and in which connections are made to the bus by forming T-junctions in the cable. Another such network is described in U.S. Pat. No. 4,199,663, in which the bus is a twisted pair of wires and connections are made inductively by means of magnetic cores, threaded through the twisted pair. The advantage of this is that it is not necessary to cut the bus or to remove any insulation from the wires in order to make a connection.
A problem with inductive coupling is that it may be difficult to ensure that the cores are connected to the bus in the correct sense. If they are connected in the wrong sense, the transmitted signals will be inverted and this may prevent correct transmission of the data. Another problem is that if the signal on the bus has a net D.C. component, this may lead to an undesirable build-up of voltage.
One object of the present invention is to overcome these problems.